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You have the solar panels protecting the lower ponds of azolla which don't like direct sun. The solar panels provide excess electricity and power any machinery used to harvest the azolla. The azolla grows over TEN TIMES as fast as grass or any other plants, so you are cycling it rapidly producing truckloads of green biomass on a monthly basis.
If it's animal feed, then the absorbed carbon is just going back into the atmosphere when the animal produces waste, dies, or gets eaten. That doesn't remove it from the cycle.